Method of making ductile high-silicon-steel sheets



Patented Dec. 10, 1929 UNITED STATES PATENT OFFICE RALPH R. CURRY, FTARENTUM, PENNSYLVANIA, ASSIGNOR '10 ALLEGHENY STEEL COMPANY, OFBRACKENRIDGE, PENNSYLVANIA, A CORPORATION VANIA.

OF PENNSYL- METHOD OF 'MAKING DUGTILE HIGH-SILICON-STEEL SHEETS NoDrawing. Application filed July 27,

This invention relates to the manufacture of silicon steel sheets suchas used in the construction of certain portions of electrical apparatusincluding the cores for transformers. Silicon steel now used in sheetform in the construction of cores for transformers and for other partsof electrical apparatus has a silicon content, as a general rule, offrom 1% to 4 depending upon the electrical roperties which are requiredin such sheets. he grades having a high silicon content, as forinstance, of from 3 to 4% are almost entirely used in the constructionof transformer cores because of their low hysteresis losses. Generallyspeaking, it is found that the higher the silicon content, the lowerwill be the hysteresis loss.

Silicon steel having a silicon content in excess of 4% when rolled intolight gauge sheets and annealed is, as a general thing, so brittle as tocause the manufacturers of such sheets to effect a compromise, in otherwords, to manufacture a silicon steel in which a portion of itselectrical value is sacrificed in favor of its ductility or malleabilitywith the result that silicon steel having a silicon content in excess of4% is seldom rolled into light gauge sheets for use in the manufactureof electrical apparatus. I.

The practice of effecting this compromlse has limited the manufacturersof such sheets to silicon steel having a maximum silicon content justshort of that from which a considerable advantage would be gained inelectrical quality, especially where the sheets are to be used inequipment operated at high flux densities.

For example, a steel having a silicon content of 4% is not as a generalrule better than a steel having a silicon content of 3.75%, but a steelhavin a silicon content of 4.25% is very materia ly better and will givematerially better results electrically than one having a silicon contentof but 4% especially if tested to high densities.

Under the ordinary methods of manufacture, a silicon steel having asilicon content of 4.25% or any silicon content in excess of 4% is sobrittle that its conversion into sheets 5 of proper thickness or gaugeentails a con- 1927. Serial No. 208,897.

siderable loss, a large percentage being bound to fail to meet thecommercial standards of ductility or malleability.

An object of this invention is to improve the present methods ofmanufacturing silicon steel sheets so that sheets having a silicon content in excess of 4% may be readily rolled into relatively thin sheetsWithout the losses now encountered because of the lack of ductility ormalleability of the sheets made under the present methods.

I have discovered that by a slight change or modification of the methodsnow utilized in the making of light gauge sheets of the higher siliconcontent steels I am able to reduce the brittleness to an extent thatwill permit the sheets to pass the commercial standard of ductility ormalleability and because of the higher silicon content an improvement inthe electrical qualities is obtained.

In the ordinary process of making silicon steel sheets for use inelectrical apparatus the ingot is rolled into sheet bars of a thicknessthat will give the required length for the gauge of sheets beingproduced. These bars are then heated to a rolling temperature and givena number of operations until the final length and gauge of the sheets isobtained.

I have found that if, after the bars have attained the rollingtemperature, they are held at that temperature for some time or soakedas the steel maker terms it, I can produce sheets that are considerablymore ductile than those produced in the regular way. In fact,-by raisingthe sheet bars of silicon steel having a silicon content of 4.25% torolling temperature and then holding them at that temperature for from 1to 4 hours and then converting these heated bars into sheets in theregular way, I obtain ductile sheets of silicon steel even though thesilicon content is as high as 4.50%.

. The improvement in the ductility or malleability of such sheets is somarked over those produced in the regular way that there is practicallyno loss for this reason.

This soaking of the sheet bars apparently permits the crystals or grainsof the steel to adjust themselves in a manner which in thesubsequentrolling to light gauge produces an arrangement of crystals or grainswhich improves the ductility of the sheets.

I have found that an excessive length of time for this soaking step isnot necessary. From one to four hours is usually sufiicient to obtainthe necessary ductility or malle ability in all cases. Sheet bars whichI have soaked for eight hours for instance, do not give measurablysofter nor more ductile sheets than those which have been soaked foronly two hours. The len th of time of soaking may be somewhat varled tomeet different requirements as to ductility or malleability, but in mostcases a soaking at rolling temperature of about two hours is foundsufficient.

Having thus described my invention, what I claim is 1. That step in theart of rolling silicon steel sheets for use in electrical apparatus,which consists in rolling sheet bars in slowly raising the temperatureof such bars to rolling temperature and in holding the same at thattemperature for at least one hour whereupon ductile relatively thinsheets may be rolled therefrom.

2. That step in the art of rolling silicon steel sheets, which consistsin rolling sheet bars from such metal in slowly raising the temperatureof such bars to rolling temperature, in holding said bars at thattemperature for at least one hour and then in rolling sheets therefrom.

3. That step in the art of rolling silicon steel sheets, which consistsin rolling sheet bars from such metal in slowl raising the temperatureof such bars to rol ing tempera ture, in holding said bars at thattemperature for about one hour and then in rolling sheets therefrom.

4. The method of making ductile silicon steel sheets having a relativelyhigh silicon content, which consists in forming an ingot of such siliconsteel, in rolling the same into sheet bars, in cutting said bars intosuitable lengths, in raising such cut bars to rolling temperature, inholding the same at substantially this temperature for at least onehour, and then in converting said bars into sheets of the requiredgauge.

5. The method of making ductile silicon steel sheets having a relativelyhigh silicon content, which consists in forming an ingot of such siliconsteel, in rolling the same into sheet bars, in cutting the bars intosuitable lengths, in raising such cut bars to rolling temperature, inholding the same at substantially this temperature for at least one hourto cause a readjustment of the grain thereof,

and then 'in converting said bars into sheets of the required gauge.

In testimony whereof, I have hereunto subscribed my. name this 22nd dayof July, 1927.

RALPH R. CURRY.

